Clostridium scindens American Type Culture Collection 35704 is capable of converting primary bile acids to toxic secondary bile acids, as well as converting glucocorticoids to androgens by side-chain cleavage. The molecular structure of the side-chain cleavage product of cortisol produced by C. scindens was determined to be 11 β-hydroxyandrost- 4-ene-3,17-dione (11 β-OHA) by high-resolution mass spectrometry, 1H and 13C NMR spectroscopy, and X-ray crystallography. Using RNA-Seq technology, we identified a cortisol-inducible ( ~ 1,000-fold) operon ( des ABCD) encoding at least one enzyme involved in anaerobic side-chain cleavage. The des C gene was cloned, overexpressed, purified, and found to encode a 20α-hydroxysteroid dehydrogenase (HSDH). This operon also encodes a putative " transketolase" ( des AB) hypothesized to have steroid-17,20-desmolase/ oxidase activity, and a possible corticosteroid transporter ( des D). RNA-Seq data suggests that the two-carbon side chain of glucocorticords may feed into the pentose-phosphate pathway and are used as a carbon source. The 20 α-HSDH is hypothesized to function as a metabolic "rheostat" controlling rates of side-chain cleavage. Phylogenetic analysis suggests this operon is rare in nature and the des C gene evolved from a gene encoding threonine dehydrogenase. The physiological effect of 11 β-OHAD on the host or other gut microbes is currently unknown.
ASJC Scopus subject areas
- Cell Biology